Ceramic glass composition

ABSTRACT

An amorphous ceramic glass composition having a density greater than about 2.1 g/cm 3  comprises: between about 35 and 55% by weight SiO 2  ; between about 18 and 28% by weight Al 2  O 3  ; between about 1 and 5% by weight CaO; between about 7 and 14% by weight MgO; between about 0.5 and 5% by weight TiO 2  ; between about 0.4 and 3% by weight B 2  O 3  ; and greater than 0 and up to about 1% by weight P 2  O 5 . A convenient source of raw materials is a mixture of coal ash waste, borax (or boric acid) manufacturing plant waste, and titanium pigment waste. The ceramic glass is formed from an intermediate ceramic mixture which is subjected to a heat treatment. The intermediate ceramic mixture is formed by heating a mixture containing SiO 2 , Al 2  O 3 , CaO, MgO, TiO 2 , B 2  O 3 , and Na 4  P 2  O 7  to a temperature between about 1400° and 1600° C.; cooling the mixture at a controlled rate between about 15° C. and about 30° C. to solidify it; annealing the mixture at a temperature between about 600° and 670° C. in an atmosphere containing oxygen; and cooling the mixture to a temperature less than about 400° C. at a cooling rate between about 15° and 30° C. per hour. The intermediate ceramic mixture is first heated to a temperature of between about 850° and 1000° C. at a heating rate of between about 1° and 2° C. per minute, and then sintered at a temperature between 850° to 1000° C. for a time period sufficient to increase its density to at least about 2.1 g/cm 3 .

This is a continuation-in-part of Ser. No. 258,845 filed Jun. 13, 1994,now abandoned, which is a division of Ser. No. 110,047 filed Aug. 20,1993 now Pat. No. 5,369,062.

FIELD OF THE INVENTION

The present invention relates generally to a ceramic composition and toa process for producing the ceramic. More specifically, the inventionrelates to a relatively dense ceramic glass exhibiting high compressiveand bending strength, high thermal resistance, and high resistance toacids and bases.

DESCRIPTION OF THE PRIOR ART

Ceramics are used in a variety of applications due to their relativelyhigh thermal and chemical resistance. Such applications include, forexample, use as containment walls for chemical reactors, and transfertubing in chemical manufacturing plants. Some ceramics have beenmanufactured using waste products as a raw material to reduce the costof the ceramic. In addition, there has recently been much interest inproviding a market for a waste product, thereby reducing the volume ofwaste that must ultimately be disposed of. For example, coal ash, whichis the waste from coal-fired electric power plants, has been used tomanufacture cast stone for the building industry. However, existingceramic products manufactured from coal ash waste are of low density(<2.1 g/cm³) and have relatively low material strength, low scratchresistance, low acid/base resistance, low impact, and low thermal shockresistance, and, therefore, limited market value. Ceramic materialshaving improved mechanical properties could find applications as, forexample, chemical laboratory counter tops and sandpaper.

Thus, there is a need for an inexpensive ceramic exhibiting improvedstrength, hardness, and chemical and mechanical resistance. There isalso a need for a ceramic that can be produced from waste materials.

SUMMARY OF THE INVENTION

This need is satisfied, the limitations of the prior art overcome, andother benefits realized in accordance with the principles of the presentinvention by a mechanically stable, amorphous ceramic composition ofhigh density (>2.1 g/cm³). The amorphous ceramic composition of thepresent invention comprises: between about 35 and 55% by weight SiO₂ ;between about 18 and 28% by weight Al₂ O₃ ; between about 1 and 5% byweight CaO; between about 7 and 14% by weight MgO; between about 0.5 and5% by weight TiO₂ ; between about 0.4 and 3% by weight B₂ O₃ ; andgreater than 0 and up to about 1% by weight P₂ O₅.

The ceramic composition may further contain between about 2 and 11% byweight Fe₂ O₃ and FeO in total, and between about 1 and 4% by weight ofK₂ O and Na₂ O in total.

A variety of raw materials may be used according to the presentinvention. However, in one specific case, the SiO₂, Al₂ O₃, and CaO areprovided by coal ash waste, the MgO is provided by the coal ash wasteand borax (or boric acid) manufacturing plant waste, the TiO₂ isprovided by the coal ash waste and titanium pigment waste, the B₂ O₃ isprovided by the borax (or boric acid) manufacturing plant waste, and theP₂ O₅ is provided by Na₄ P₂ O₇.

In one example the ceramic glass has the following properties: a densityof about 2.6 g/cm³ ; a compressive strength of about 800 kg/cm² ; abending strength of about 937 kg/cm², an impact resistance of 20kg-cm/cm² ; a thermal shock resistance of about 700° C. and a Mohshardness about the same as corundum.

The ceramic glass of the invention is produced by forming anintermediate ceramic mixture and then subjecting it to a heat treatment.The intermediate ceramic mixture is formed in a first approach by thefollowing steps: providing an initial process mixture containing SiO₂,Al₂ O₃, CaO, MgO, TiO₂, B₂ O₃, and Na₄ P₂ O₇ ; heating the processmixture to a temperature between about 1400° and 1600° C.; cooling theprocess mixture from this temperature at a controlled rate between about15° and about 30° C. per hour to a lower temperature sufficient tosolidify the process mixture, generally less than about 650° C.;annealing the process mixture, following the step of cooling, at atemperature between about 600° and 670° C. in an atmosphere containingoxygen and for a time period greater than about 3.5 hours; and coolingthe process mixture, following annealing, to a temperature less thanabout 400° C. at a cooling rate between about 15° and about 30° C. perhour. Both cooling steps at the controlled rates are necessary in orderto produce a high density amorphous ceramic glass product. If thecooling rate is not strictly controlled, the ultimate product does notbecome fully consolidated and exhibits inferior physical properties; inparticular, the density is less than 2.1 g/cm³ and the compressivestrength, bending strength and impact resistance are below thosedescribed above. The process mixture may next be molded, as discussedbelow, or directly subjected to the heat treatment.

In a second approach the intermediate ceramic mixture is formed by a setof steps similar to the above. However, under the second approach, theNa₄ P₂ O₇ is added to the process mixture, for example, following thestep of cooling to a temperature less than about 400° C. It should benoted that the Na₄ P₂ O₇ may be added anytime after the initial step ofheating the process mixture. The addition of Na₄ P₂ O₇ to the processmixture permits the intermediate ceramic mixture to be shaped or molded,but its addition is not necessary when performing the abovementionedcooling steps which increase the density of the final product. Further,before adding the Na₄ P₂ O₇, the process mixture is heated to atemperature greater than about 1300° C., but less than the temperatureused in the step of heating the initial process mixture to a temperaturebetween about 1400° and 1600° C. This is in contrast to the firstapproach in which the Na₄ P₂ O.sub. 7 is added to the initial processmixture.

Like the first approach, the process mixture may next be molded, asdiscussed further below, or directly subjected to the heat treatment.Where the process mixture is to be molded, the Na₄ P₂ O₇ addition can beperformed either as a part of the heating of the process mixture inpreparation for pouring into a mold or prior thereto.

In both the first and second approaches for forming the intermediatemixture, the process mixture may be molded to a desired shape prior tothe heat treatment. However, in some applications this may not benecessary, and the process mixture is subjected to the heat treatmentwithout any molding thereof. Where molding is performed, the processmixture is heated to a temperature sufficient to liquify the processmixture for pouring into a mold, but less than the temperature used inthe step of heating the initial process mixture to a temperature betweenabout 1400° and 1600° C.

After forming the intermediate ceramic mixture by the first or secondapproach discussed above (whether molded or not), the ceramic mixture issubjected to a heat treatment. The heat treatment increases the densityof the intermediate ceramic mixture, which may initially, for example,have a density of less than about 2.1 g/cm³, to a density greater than,for example, about 2.5 g/cm³. The heat treatment has two steps. In thefirst step, the ceramic mixture is heated to a temperature of betweenabout 850° and 1000° C. at a heating rate of between about 1° and 2° C.per minute. In the second step, the ceramic mixture is sintered at atemperature between about 850° and 1000° C. for a time period sufficientto increase the density of the ceramic mixture to at least about 2.1g/cm³.

The ceramic glass of the present invention is amorphous, of high density(>2.1 g/cm³), and mechanically stable. In particular, due to its highdensity, the composition has improved hardness, chemical resistance,thermal shock resistance, and material strength relative to conventionalceramics. Other advantages of the present invention include improvedimpact resistance and compressive strength. Visibly, the ceramic glassof the present invention is opaque and differs from similar less densecompositions in its shiny, glossy appearance.

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The properties and formation of a ceramic according to the presentinvention are described below. Thereafter, additional description isprovided on some uses and applications for this ceramic.

I. Properties of the Final Ceramic Product

The final amorphous ceramic product (hereinafter referred to as theceramic glass) formed according to the method of the present inventionhas a density greater than about 2.1 g/cm³, and comprises: between about35 and 55% by weight SiO₂ ; between about 18 and 28% by weight Al₂ O₃ ;between about 1 and 5% by weight CaO; between about 7 and 14% by weightMgO; between about 0.5 and 5% by weight TiO₂ ; between about 0.4 and 3%by weight B₂ O₃ ; and greater than 0 and up to about 1% by weight P₂ O₅.These components of the ceramic glass, when combined using the method ofthe present invention, are necessary to provide an amorphous product ofhigh density having useful properties. By contrast, compositions of lowdensity comprised of the same components provide a material that ismerely a mixture having little mechanical integrity.

The B₂ O₃ in the ceramic glass improves the hardness of the material,and the P₂ O₅ reduces the viscosity of the process mixture during themolding process. Without the addition of P₂ O₅, the resulting productretains its high density, but the composition cannot be shaped.

Other components, however, may be present in the ceramic glass withoutsubstantially affecting its properties. For example, the ceramic glassmay further contain between about 2 and 11% by weight Fe₂ O₃ and FeO intotal, and between about 1 and 4% by weight of K₂ O and Na₂ O in total.In addition, many other inert components may be present in the finalceramic glass, and it is expected that their presence will notsubstantially affect the properties of the ceramic glass. Theseadditional components are sometimes present in the final ceramic glasssimply by virtue of their presence in one of the initial raw materials.

In general, a variety of raw materials may be used to form the ceramicglass. Specific examples of raw materials that may be used are discussedfurther herein. In the preferred embodiment, the P₂ O₅ is provided froma raw material of Na₄ P₂ O₇ since P₂ O₅ has a relatively low boilingpoint and would otherwise evaporate during processing.

In one specific case, which is advantageous because it allows therecycling of some industrial waste products, the SiO₂, Al₂ O₃, and CaOmay be provided by coal ash waste, the MgO may be provided by the coalash waste and borax (or boric acid) manufacturing plant waste (the boraxwaste may be either solid or mud waste), the TiO₂ may be provided by thecoal ash waste and titanium pigment waste, the B₂ O₃ may be provided bythe borax (or boric acid) manufacturing plant waste. Note, as mentionedabove, that the P₂ O₅ is provided by Na₄ P₂ O₇. The use of these wastesas raw materials and the processing steps for forming the ceramic glassare discussed further below. When coal ash waste is used as a rawmaterial, Fe₂ O₃, FeO, K₂ O, and Na₂ O, are also components of the finalceramic glass because of their initial presence in the coal ash wasteused as a raw material.

Although the ceramic according to the present invention is referred toas a "ceramic glass" the scope of the present invention is not intendedto be limited by the use of the word "glass". Instead, the term "ceramicglass" is merely a shorthand way to describe the ceramic according tothe present invention in terms of some of its properties. For example,the ceramic according to the present invention is neither crystallinenor polycrystalline as has been determined by electron diffraction, butis instead an amorphous solid similar in some microstructural aspects tosilicate glass. The ceramic glass does not have a single, fixed meltingpoint, but rather starts melting between about 800° and 900° C. Inaddition, the ceramic glass is referred to as a ceramic because itsmajor constituents are metallic oxides.

The ceramic glass formed by the method of the present invention exhibitsseveral desirable properties due to its high density, such as improvedmechanical strength, acid and base resistance, and hardness relative toconventional ceramics. More specifically, as a non-limiting example, oneceramic glass was formed with the following properties:

a density of about 2.6 g/cm³ ;

a compressive strength of about 800 kg/cm² ;

a bending strength of about 937 kg/cm² ;

a thermal shock resistance of about 700° C.;

a Mohs hardness of about 9;

an acid resistance of 99% against 98% H₂ SO₄, and 90% against 20% H₂ SO₄;

an alkaline resistance of 90% against 20% NaOH; and

an impact resistance of 20 kg-cm/cm².

More generally, other ceramic glasses formed by the method of thepresent invention have exhibited the following properties:

a density of about 2.1 to 2.6 g/cm³

a compressive strength of about 700 to 800 kg/cm² ;

a bending strength of about 900 to 937 kg/cm² ;

a thermal shock resistance of about 600° to 750° C.; and

a Mohs hardness of about 8 to 9.

With respect to the Mohs hardness above, corundum is defined to have ahardness value of 9 and diamond a hardness value of 10. The mechanicaltests above are standard tests in the art of materials testing. The acidand base resistance tests are conducted in accordance with ASTMstandards.

The high density ceramic glass manufactured in accordance with themethod of the present invention using the above-described wastematerials (specifically, including coal ash), is an amorphous opaquesolid exhibiting a shiny black color. By contrast, in appearance, lowdensity compositions produced using the same components form a materialhaving a dull black finish.

The black color exhibited by the compositions is believed to be due tothe iron oxides from the coal ash that are present in the final ceramicglass product. This hypothesis is supported by the formation of a whiteceramic glass containing the necessary components described above, butlacking iron oxides.

II. Formation of the Ceramic Glass

The high density ceramic glass of the present invention is produced,first, by forming an intermediate ceramic mixture and, second, bysubjecting the intermediate mixture to a heat treatment. There are twoapproaches for forming the intermediate ceramic mixture. These arediscussed in turn below, followed by a discussion of the heat treatment.

A. First Approach for Forming the Intermediate Ceramic Mixture

For both the first and second approaches, the intermediate ceramicmixture formed must contain the following critical components insubstantially the same percentages as in the final ceramic glass: SiO₂,Al₂ O₃, CaO, MgO, TiO₂, B₂ O₃, and P₂ O₅. In the first step of the firstapproach, the raw materials are combined to provide a process mixturecomprising the following critical components: SiO₂, Al₂ O₃, CaO, MgO,TiO₂, B₂ O₃, and Na₄ P₂ O₇. These components are combined as necessaryso that the intermediate ceramic mixture substantially will contain thecritical component percentages described above for the final ceramicglass. Some Na₄ P₂ O₇ must be added to the process mixture to providethe P₂ O₅ in the final ceramic glass, and in general Na₄ P₂ O₇ forms upto about 2% by weight thereof. The Na₄ P₂ O₇ reduces the viscosity ofthe process mixture during the molding process which in pouring themixture for molding. The process mixture may contain other components inaddition to the critical components so long as the above relativeproportions for the critical components are substantially not changed.

In one example, coal ash waste, borax manufacturing plant waste,titanium pigment waste, and Na₄ P₂ O₇ are used as raw materials. Thecoal ash waste, which is typically produced by coal-fired electric powerplants, forms 70% by weight of the process mixture. The boraxmanufacturing plant waste forms about 26% by weight thereof, and thetitanium pigment waste forms about 3.7% by weight thereof. About 0.3% byweight of Na₄ P₂ O₇ is also added.

The coal ash waste typically contains SiO₂, Al₂ O₃, CaO, MgO, TiO₂, Fe₂O₃, FeO, K₂ O, and Na₂ O. Because the coal ash waste does not usuallycontain sufficient MgO for the ceramic glass, the borax manufacturingplant waste, which contains between about 30 and 40% by weight MgO, isan additional source of MgO for the ceramic glass. Also, the titaniumpigment waste, which contains between about 5 and 15% by weight TiO₂, isused as a second source of TiO₂.

Several types of coal ash waste may be used. One specific example isbrown coal ash waste. Brown coal is predominantly used in Europe andtypically contains a greater proportion of CaO than coal in the UnitedStates. However, this is not expected to affect the practice of theinvention as long as the final proportion of CaO in the ceramic glassfalls within the ranges above.

After mixing the raw materials, the process mixture is heated to a firstintermediate forming temperature which is generally between about 1400°and 1600° C., and more preferably between 1400° and 1500° C.

Next, the process mixture is cooled at a controlled rate generallybetween about 15° and about 30° C. per hour, and more preferably betweenabout 15° and 25° C. per hour to a second intermediate formingtemperature sufficiently low to solidify the process mixture so as toproduce a substantially uniform product. This temperature is generallyabout 650° C. or lower, and may be as low as room temperature. Coolingrates greater than about 30° C. per hour or less than about 15° C. perhour will result in a final product having a density less than about 2.1g/cm³.

After the cooling above, the process mixture is annealed at an annealingtemperature between about 600° and 670° C. The annealing time period isgenerally greater than about 3.5 hours, and more preferably betweenabout 3.5 and 5 hours. During annealing, the process mixture is exposedto an oxygen-containing ambient so that all critical components are inthe form of oxides.

Following annealing, the process mixture is cooled to a thirdintermediate forming temperature generally less than about 400° C., andmore preferably between about 300° and 350° C. This cooling is performedfrom the annealing temperature at a rate generally between about 15° andless than about 30° C. per hour, and preferably between about 15° and25° C. per hour. The process mixture at this point has a fixed shape andis substantially a single piece of material. Cooling rates greater thanabout 30° C. per hour or less than about 15° C. per hour will result ina less dense product.

Next, the process mixture may either be directly subjected to a heattreatment or be molded prior thereto. If molded, the process mixture isheated to a molding temperature generally sufficient to liquify theprocess mixture for pouring into a mold, but less than the temperaturebetween 1400° and 1600° C. used for heating the initial process mixtureabove. Preferably the molding temperature is between about 1360° and1400° C. Prior to molding, the process mixture may be cooled to aboutroom temperature following annealing above. However, this is notnecessary. Following molding, the process mixture is subjected to theheat treatment described below in section C.

B. Second Approach for Forming the Intermediate Ceramic Mixture

The second approach for forming the intermediate ceramic mixture issubstantially similar to the first approach except that the Na₄ P₂ O₇ isadded closer to the molding step (or the heat treatment where no moldingis performed). The inclusion of Na₄ P₂ O₇ in the initial process mixtureis not necessary to obtain a high density product. The purpose of addingNa₄ P₂ O₇, and thereby P₂ O₅, is to assist in the molding or shaping ofthe ceramic glass. Thus, the Na₄ P₂ O₇ may be added to the mixture in alater step. For ease in understanding, much of the process descriptionfor the first approach is presented again below, as modified whereappropriate.

In the first step of the second approach, the raw materials are combinedto provide a process mixture comprising the following criticalcomponents: SiO₂, Al₂ O₃, CaO, MgO, TiO₂, and B₂ O₃. Note that Na₄ P₂ O₇is not added at this point. As in the first approach, the processmixture may use a variety of raw materials and contain other componentsin addition to the critical components.

After mixing the raw materials, the process mixture is heated to a firstintermediate forming temperature which is generally between about 1400°and 1600° C., and preferably between about 1400° and 1500° C.

Next, the process mixture is cooled at a controlled rate between about15° and about 30° C. per hour, preferably between about 15° and 25° C.per hour, to a second intermediate forming temperature sufficiently lowto solidify the process mixture. This temperature is generally about650° C. or lower, and may be about room temperature.

After the cooling above, the process mixture is annealed at an annealingtemperature between about 600° and 670° C. The annealing time period isgenerally greater than about 3.5 hours, and more preferably betweenabout 3.5 and 5 hours. During annealing, the process mixture is exposedto an oxygen-containing atmosphere.

Following annealing, the process mixture is cooled to a thirdintermediate forming temperature generally less than about 400° C., andpreferably between about 300° and 350° C. This cooling is performed fromthe annealing temperature at a rate generally between about 15° and 30°C. per hour, and preferably between about 15° and 25° C. per hour. Theprocess mixture at this point has a fixed shape and is substantially asingle piece of material.

Next, as in the first approach, the process mixture may either bedirectly subjected to a heat treatment or be molded prior thereto.However, for the second approach, in order to produce the ceramic glassof the present invention, Na₄ P₂ O₇ must be added to the process mixturebefore employing the heat treatment process, preferably following theabove step of cooling after annealing. The Na₄ P₂ O₇ is added to theprocess mixture at a temperature generally greater than about 1300° C.,and more preferably greater than about 1350° C., but less than thetemperature between 1400° and 1600° C. used for heating the initialprocess mixture above. Where molding will be performed, the Na₄ P₂ O₇can be added during the heating in preparation for molding. Generally,up to about 2% by weight of Na4P₂ O₇ is added to the process mixture,and more preferably about 0.3% is added. The Na₄ P₂ O₇ is the source ofP₂ O.sub. 5 in the final ceramic glass and reduces the viscosity of theprocess mixture during the molding process to make the mixture easier topour into a mold.

If the process mixture will be molded, it is heated to a moldingtemperature generally sufficient to liquify the process mixture forpouring into a mold, but less than the temperature between 1400° C. and1600° C. used for heating the initial process mixture above. Preferablythe molding temperature between about 1360° and 1400° C. Prior tomolding, the process mixture may be cooled to about room temperaturefollowing annealing above. Following molding, the process mixture issubjected to the heat treatment described below.

A non-limiting example of the composition of an intermediate ceramicmixture that has been formed is the following: 46.82% SiO₂, 26.66% Al₂O₃, 4.05% Fe₂ O₃, 4.10% FeO, 2.37% CaO, 11.14% MgO, 0.71% K₂ O, 0.96%Na₂ O, 1.76% TiO₂, 0.89% B₂ O₃, and 0.35% P₂ O₅, all by weight. Thesepercentages were determined by chemical analysis.

C. Heat Treatment of the Intermediate Ceramic Mixture to Produce CeramicGlass

After forming the intermediate ceramic mixture by either the first orsecond approach discussed above, the intermediate ceramic mixture issubjected to a heat treatment. The heat treatment is necessary forincreasing the density of the intermediate ceramic mixture. It is thisincrease in density which gives the final ceramic glass its most usefulproperties.

In general, the heat treatment has two steps. In the first step, theintermediate ceramic mixture is heated from a temperature generally lessthan 980° C., and more preferably less than 910° C., to a first heattreatment temperature generally between about 850° and 1000° C., andmore preferably between about 900° and 1000° C., at a heating rategenerally between about 1° and 2° C. per minute, and more preferablybetween about 1° and 1.5° C. per minute. The intermediate ceramicmixture may be heated from about room temperature, if desired, althougha higher starting temperature, as just described, is acceptable.

In the second step, the intermediate ceramic mixture is sintered at asintering temperature generally between about 850° and 1000° C., andmore preferably between about 900° and 1000° C. Prior to sintering, theintermediate ceramic mixture has a density of less than about 2.1 g/cm³.Sintering is performed for a time period sufficient to increase thedensity of the ceramic mixture to at least about 2.1 g/cm³, and morepreferably to about 2.5 g/cm³. The optimum density is about 2.6 g/cm³.This time period is generally between about 2.5 and 4.0 hours, and morepreferably. between about 2.5 and 3.5 hours. The optimum time period isabout 3 hours. Time periods longer than this were not found tosubstantially increase the density of the ceramic mixture. Time periodsless than 2.5 hours were found to result in a lower density. Thesintering temperature may be substantially the same as or different fromthe final temperature achieved following the first step of heatingabove.

After sintering, the ceramic mixture is cooled to a temperaturegenerally less than about 910° C. The rate of cooling is not critical,and the mixture may also be allowed to cool to room temperaturenaturally.

As mentioned above, the two cooling steps of the intermediate ceramicglass production process must be done at controlled rates in order toobtain an amorphous ceramic glass product of high density. Addition ofNa₄ P₂ O₇ to the initial process mixture is not necessary to increaseproduct density during the cooling steps, and thus Na₄ P₂ O₇ may beadded later. However, the sintering step of the heat treatment isnecessary to yield a high density ceramic glass. If either cooling stepor the sintering step is omitted, the product formed, although it willhave the same composition as the ceramic glass, will be a low density(less than 2.1 g/cm³) mixture, which is mechanically unstable andcrumbles. By contrast, the ceramic glass produced by the method of thepresent invention is an amorphous solid. In appearance, a low densitycomposition exhibits a dull opaque finish, whereas the ceramic glass ofthe present invention is shiny. Finally, a low density product does notexhibit the desirable mechanical and chemical properties characteristicof the ceramic glass formed using the method of the present invention.

III. EXAMPLES

The present invention is further illustrated in the examples givenbelow. These examples are provided for the purpose of description, andthe details provided therein are not intended to limit the scope of thepresent invention.

EXAMPLE 1

An initial process mixture was formed by mixing about 70% by weight ofcoal ash waste, about 25% by weight of solid borax manufacturing plantwaste, about 4% by weight of waste from a titanium pigment manufacturingplant, and about 1% by weight of Na₄ P₂ O₇. After mixing, thecomposition of the mixture was as follows:

    ______________________________________                                                              Percentage                                              Component             (by weight)                                             ______________________________________                                        SiO.sub.2             51                                                      Al.sub.2 O.sub.3      23                                                      Fe.sub.2 O.sub.3 and FeO                                                                            8                                                       CaO                   3.5                                                     MgO                   7.5                                                     K.sub.2 O             1                                                       Na.sub.2 O            1                                                       TiO.sub.2             2                                                       B.sub.2 O.sub.3       2.5                                                     P.sub.2 O.sub.5 (as a component of Na.sub.4 P.sub.2 O.sub.7)                                        0.3                                                     ______________________________________                                    

An intermediate ceramic mixture was then formed as follows: the processmixture was heated from room temperature to 1500° C., cooled to 640° C.at a rate of 25° C./hour, annealed at 640° C. for 4 hours, cooled to320° C. at a rate of 25° C. per hour, and then cooled from 320° C. toroom temperature. A ceramic glass was then formed as follows: theintermediate ceramic mixture was heated to 950° C. at 1.0° C. perminute, sintered at 950° C. for 2.5 hours, and then cooled to roomtemperature. The ceramic glass thus formed had properties similar tothose described above.

EXAMPLE 2

An initial process mixture was formed by mixing about 70% by weight ofcoal ash waste, about 25% by weight of solid borax manufacturing plantwaste, about 4% by weight of waste from a titanium pigment manufacturingplant, and about 1% by weight of Na₄ P₂ O₇. After mixing, thecomposition of the mixture was as follows:

    ______________________________________                                                              Percentage                                              Component             (by weight)                                             ______________________________________                                        SiO.sub.2             50                                                      Al.sub.2 O.sub.3      23                                                      Fe.sub.2 O.sub.3 and FeO                                                                            8                                                       CaO                   3.0                                                     MgO                   9.5                                                     K.sub.2 O             0.8                                                     Na.sub.2 O            1                                                       TiO.sub.2             2                                                       B.sub.2 O.sub.3       2.5                                                     P.sub.2 O.sub.5 (as a component of Na.sub.4 P.sub.2 O.sub.7)                                        0.3                                                     ______________________________________                                    

An intermediate ceramic mixture was then formed as follows: the processmixture was heated from room temperature to 1480° C., cooled to 600° C.at a rate of 25° C./hour, annealed at 600° C. for 4.5 hours, cooled to300° C. at a rate of 25° C. per hour, and then cooled from 300° C. toroom temperature. A ceramic glass was then formed as follows: theintermediate ceramic mixture was heated to 930° C. at 1.0° C. perminute, sintered at 930° C. for 3.0 hours, and then cooled to roomtemperature. The ceramic glass thus formed had a significantly improvedalkaline resistance of 95% against 35% NaOH. Other properties weresimilar to those described above.

EXAMPLE 3

An initial process mixture was formed by mixing about 70% by weight ofcoal ash waste, about 25% by weight of solid borax manufacturing plantwaste, about 4% by weight of waste from a titanium pigment manufacturingplant, and about 1% by weight of Na₄ P₂ O₇. After mixing, thecomposition of the mixture was as follows:

    ______________________________________                                                              Percentage                                              Component             (by weight)                                             ______________________________________                                        SiO.sub.2             50                                                      Al.sub.2 O.sub.3      23                                                      Fe.sub.2 O.sub.3 and FeO                                                                            9                                                       CaO                   3.2                                                     MgO                   8.2                                                     K.sub.2 O             0.9                                                     Na.sub.2 O            1                                                       TiO.sub.2             2                                                       B.sub.2 O.sub.3       2.5                                                     P.sub.2 O.sub.5 (as a component of Na.sub.4 P.sub.2 O.sub.7)                                        0.3                                                     ______________________________________                                    

An intermediate ceramic mixture was then formed as follows: the processmixture was heated from room temperature to 1460° C., cooled to 630° C.at a rate of 25° C./hour, annealed at 630° C. for 4 hours, cooled to310° C. at a rate of 25° C. per hour, and then cooled from 310° C. toroom temperature. A ceramic glass was then formed as follows: theintermediate ceramic mixture was heated to 940° C. at 1.0° C. perminute, sintered at 940° C. for 3.5 hours, and then cooled to roomtemperature. The ceramic glass thus formed had properties similar tothose described above.

EXAMPLE 4

An initial process mixture was formed by mixing about 70% by weight ofcoal ash waste, about 25% by weight of solid borax manufacturing plantwaste, about 4% by weight of waste from a titanium pigment manufacturingplant, and about 1% by weight of Na₄ P₂ O₇. After mixing, thecomposition of the mixture was as follows:

    ______________________________________                                                              Percentage                                              Component             (by weight)                                             ______________________________________                                        SiO.sub.2             50                                                      Al.sub.2 O.sub.3      23                                                      Fe.sub.2 O.sub.3 and FeO                                                                            8                                                       CaO                   3                                                       MgO                   10.5                                                    K.sub.2 O             1                                                       Na.sub.2 O            1                                                       TiO.sub.2             2                                                       B.sub.2 O.sub.3       0.9                                                     P.sub.2 O.sub.5 (as a component of Na.sub.4 P.sub.2 O.sub.7)                                        0.3                                                     ______________________________________                                    

An intermediate ceramic mixture was then formed as follows: the processmixture was heated from room temperature to 1500° C., cooled to 600° C.at a rate between about 15° and 30° C. per hour, annealed at 600° C. for5 hours, cooled to 300° C. at 20° C. per hour (this took about 15hours), and then cooled from 300° C. to room temperature. A ceramicglass was then formed as follows: the intermediate ceramic mixture washeated to 950° C. at 1.0° C. per minute, sintered at 950° C. for 2.5hours, and then cooled to room temperature. The ceramic glass thusformed had properties similar to those described above.

EXAMPLE 5

An initial process mixture was formed by mixing about 70% by weight ofcoal ash waste, about 25% by weight of solid borax manufacturing plantwaste, about 4% by weight of waste from a titanium pigment manufacturingplant, and about 1% by weight of Na₄ P₂ O₇. After mixing, thecomposition of the mixture was as follows:

    ______________________________________                                                              Percentage                                              Component             (by weight)                                             ______________________________________                                        SiO.sub.2             52                                                      Al.sub.2 O.sub.3      20                                                      Fe.sub.2 O.sub.3 and FeO                                                                            9                                                       CaO                   3.5                                                     MgO                   10.0                                                    K.sub.2 O             1                                                       Na.sub.2 O            1                                                       TiO.sub.3             2                                                       B.sub.2 O.sub.3       0.9                                                     P.sub.2 O.sub.5 (as a component of Na.sub.4 P.sub.2 O.sub.7)                                        0.3                                                     ______________________________________                                    

An intermediate ceramic mixture was then formed as follows: the processmixture was heated from room temperature to 1500° C., cooled to 650° C.at a rate between about 15° and about 30° C. per hour, annealed at 650°C. for 4 hours, cooled to 300° C. at 20° C. per hour, and then cooledfrom 300° C. to room temperature. A ceramic glass was then formed asfollows: the intermediate ceramic mixture was heated to 910° C. at 1.5°C. per minute, sintered at 910° C. for 3.0 hours, and then cooled toroom temperature. The ceramic glass thus formed had properties similarto those described above.

EXAMPLE 6

An initial process mixture was formed by mixing about 70% by weight ofcoal ash waste, about 25% by weight of solid borax manufacturing plantwaste, about 4% by weight of waste from a titanium pigment manufacturingplant, and about 1% by weight of Na₄ P₂ O₇. After mixing, thecomposition of the mixture was as follows:

    ______________________________________                                                              Percentage                                              Component             (by weight)                                             ______________________________________                                        SiO.sub.2             50                                                      Al.sub.2 O.sub.3      25                                                      Fe.sub.2 O.sub.3 and FeO                                                                            8                                                       CaO                   2.5                                                     MgO                   9.0                                                     K.sub.2 O             1                                                       Na.sub.2 O            1                                                       TiO.sub.2             2                                                       B.sub.2 O.sub.3       0.9                                                     P.sub.2 O.sub.5 (as a component of Na.sub.4 P.sub.2 O.sub.7)                                        0.3                                                     ______________________________________                                    

An intermediate ceramic mixture was then formed as follows: the processmixture was heated from room temperature to 1450° C., cooled to 650° C.at a rate between about 15° and 30° C. per hour, annealed at 650° C. for4 hours, cooled to 300° C. at 20° C. per hour, and then cooled from 300°C. to room temperature. A ceramic glass was then formed as follows: theintermediate ceramic mixture was heated to 910° C. at 1.0° C. perminute, sintered at 910° C. for 3.0 hours, and then cooled to roomtemperature. The ceramic glass thus formed had properties similar tothose described above.

EXAMPLE 7

An initial process mixture was formed by mixing about 70% by weight ofcoal ash waste, about 25% by weight of solid borax manufacturing plantwaste, about 4% by weight of waste from a titanium pigment manufacturingplant, and about 1% by weight of Na₄ P₂ O₇. After mixing, thecomposition of the mixture was as follows:

    ______________________________________                                                              Percentage                                              Component             (by weight)                                             ______________________________________                                        SiO.sub.2             53                                                      Al.sub.2 O.sub.3      22                                                      Fe.sub.2 O.sub.3 and FeO                                                                            8                                                       CaO                   3                                                       MgO                   8                                                       K.sub.2 O             1                                                       Na.sub.2 O            1                                                       TiO.sub.2             2.5                                                     B.sub.2 O.sub.3       1.0                                                     P.sub.2 O.sub.5 (as a component of Na.sub.4 P.sub.2 O.sub.7)                                        0.25                                                    ______________________________________                                    

An intermediate ceramic mixture was then formed as follows: the processmixture was heated from room temperature to 1500° C., cooled to 650° C.at a rate between about 15° and about 30° C. per hour, annealed at 650°C. for 4.5 hours, cooled to 350° C. at 20° C. per hour, and then cooledfrom 350° C. to room temperature. A ceramic glass was then formed asfollows: the intermediate ceramic mixture was heated to 950° C. at 1.5°C. per minute, sintered at 950° C. for 3.0 hours, and then cooled toroom temperature. The ceramic glass thus formed had properties similarto those described above.

EXAMPLE 8

An initial process mixture was formed by mixing about 70% by weight ofcoal ash waste, about 25% by weight of solid borax manufacturing plantwaste, about 4% by weight of waste from a titanium pigment manufacturingplant, and about 1% by weight of Na₄ P₂ O₇. After mixing, thecomposition of the mixture was as follows:

    ______________________________________                                                              Percentage                                              Component             (by weight)                                             ______________________________________                                        SiO.sub.2             40                                                      Al.sub.2 O.sub.3      25                                                      Fe.sub.2 O.sub.3 and FeO                                                                            8.5                                                     CaO                   5                                                       MgO                   10                                                      K.sub.2 O             1.5                                                     Na.sub.2 O            2.5                                                     TiO.sub.2             3.5                                                     B.sub.2 O.sub.3       3.0                                                     P.sub.2 O.sub.5 (as a component of Na.sub.4 P.sub.2 O.sub.7)                                        0.5                                                     ______________________________________                                    

An intermediate ceramic mixture was then formed as follows: the processmixture was heated from room temperature to 1400° C., cooled to 650° C.at a rate between about 15° and 30° C. per hour, annealed at 650° C. for4 hours, cooled to 350° C. at 20° C. per hour, and then cooled from 350°C. to room temperature. A ceramic glass was then formed as follows: theintermediate ceramic mixture was heated to 910° C. at 1.5° C. perminute, sintered at 910° C. for 3.0 hours, and then cooled to roomtemperature. The ceramic glass thus formed had properties similar tothose described above.

IV. Uses and Applications of the Ceramic Glass

The ceramic glass according to the present invention has a number ofuseful applications. The following are a representative sample of suchapplications:

laboratory counter tops;

sandpaper and other grits;

wear-resistant artificial stones including decorative stones;

chemical reaction stills;

fluid transfer tubing;

replacements for cast iron or steel piping and glass fiber;

matrix composites for manufacturing glass steel in, for example, coolingtowers and yacht bodies;

glassware;

abrasive resistant liners;

glasswares and methods of coloring same;

replacements for aluminum or aluminum alloys in, for example,construction frameworks; and

solar energy absorption elements.

Although the present invention has been described in detail above, it isnot intended to be limited to the specific form set forth herein, but,on the contrary, it is intended to cover such alternatives andequivalents as can reasonably be included within the spirit and scope ofthe invention as defined by the appended claims.

For example, in other embodiments according to the present invention,the color of the ceramic mixture could be changed by adding a variety ofoxides, depending upon the particular color desired. Also, the hardnesscould be reduced by decreasing either the B₂ O₃ or TiO₂ components.

We claim:
 1. A process for producing an amorphous ceramic glass having adensity greater than about 2.1 g/cm³, said process comprising the stepsof:(a) forming an intermediate ceramic mixture comprising SiO₂, Al₂ O₃,CaO, MgO, TiO₂, B₂ O₃, and P₂ O₅, wherein said step of forming anintermediate ceramic mixture comprises the steps of: (a1) providing aprocess mixture comprising SiO₂, Al₂ O₃, CaO, MgO, TiO₂, B₂ O₃, and Na₄P₂ O₇ ; (a2) heating said process mixture to a first intermediateforming temperature between about 1400° and 1600° C.; (a3) cooling saidprocess mixture from said first intermediate forming temperature at acooling rate between about 15° and about 30° C. per hour to a secondintermediate forming temperature sufficient to solidify said processmixture; (a4) annealing said process mixture, following said step ofcooling from said first intermediate forming temperature, at anannealing temperature between about 600° and 670° C. in an atmospherecontaining oxygen and for a time period greater than about 3.5 hours;and (a5) cooling said process mixture from said annealing temperature toa third intermediate forming temperature less than about 400° C. at acooling rate between about 15° and about 30° C. per hour; and (b)subjecting said intermediate ceramic mixture to a heat treatmentcomprising the steps of: (b1) heating said intermediate ceramic mixtureto a first heat treatment temperature of between about 850° and 1000° C.at a heating rate of between about 1° and 2° C. per minute; and (b2)sintering said intermediate ceramic mixture at a sintering temperaturebetween about 850° and 1000° C. for a time period sufficient to increasethe density of said ceramic mixture to at least about 2.1 g/cm³.
 2. Theprocess of claim 1 wherein said first intermediate forming temperatureis between about 1400° and 1500° C.
 3. The process of claim 1 whereinsaid second intermediate forming temperature is about room temperature.4. The process of claim 1 wherein said time period of said annealingstep (a4) is between about 3.5 and 5 hours,
 5. The process of claim 1wherein said third intermediate forming temperature is between about300° and 350° C.
 6. The process of claim 1 wherein said intermediateceramic mixture is heated to said first heat treatment temperature fromabout room temperature.
 7. The process of claim 1 wherein said timeperiod of said sintering step (b2) is between about 2.5 and 4 hours. 8.The process of claim 1 wherein said heat treatment further comprises thestep of cooling said intermediate ceramic mixture to a temperature lessthan about 910° C. following said heat treatment.
 9. The process ofclaim 1 wherein said amorphous ceramic glass has a density greater thanabout 2.5 g/cm³ following said heat treatment.
 10. The process of claim1 wherein said process mixture comprises coal ash waste; a wastematerial comprising borax or boric acid manufacturing plant waste; andtitanium pigment waste.
 11. The process of claim 1 wherein said processmixture further comprises between about 1 and 4% by weight of K₂ O andNa₂ O in total, and between 2 and 11% by weight Fe₂ O₃ and FeO in total.12. The process of claim 1 further comprising the step of molding saidintermediate process mixture at a molding temperature sufficient toliquify said process mixture for pouring into a mold but less than saidfirst intermediate forming temperature, said step of molding followingsaid step (a5) of cooling from said annealing temperature.
 13. Theprocess of claim 12 wherein said molding temperature is between about1360° and 1400° C.
 14. The process of claim 12 further comprising a stepof cooling said process mixture to about room temperature following saidstep (a5) of cooling from said annealing temperature but prior to saidstep of molding.
 15. The process of claim 1 wherein said intermediateceramic mixture comprises:between about 35 and 55% by weight SiO₂ ;between about 18 and 28% by weight Al₂ O₃ between about 1 and 5% byweight CaO; between about 7 and 14% by weight MgO; between about 0.5 and5% by weight TiO₂ ; between about 0.4 and 3% by weight B₂ O₃ ; andgreater than 0 and up to about 1% by weight P₂ O₅.
 16. The process ofclaim 1 wherein said process mixture comprises:between about 35 and 55%by weight SiO₂ ; between about 18 and 28% by weight Al₂ O₃ ; betweenabout 1 and 5% by weight CaO; between about 7 and 14% by weight MgO;between about 0.5 and 5% by weight TiO₂ ; between about 0.4 and 3% byweight B₂ O₃ ; and greater than 0 and up to about 2% by weight Na₄ P₂O₇.
 17. A process for producing an amorphous ceramic glass having adensity greater than about 2.1 g/cm³, said process comprising the stepsof:(a) forming an intermediate ceramic mixture comprising SiO₂, Al₂ O₃,CaO, MgO, TiO₂, B₂ O₃, and P₂ O₅, wherein said step of forming anintermediate ceramic mixture comprises the steps of: (a1) providing aprocess mixture comprising SiO₂, Al₂ O₃, CaO, MgO, TiO₂, and B₂ O₃ ;(a2) heating said process mixture to a first intermediate formingtemperature between about 1400° and 1600° C.; (a3) cooling said processmixture from said first intermediate forming temperature at a coolingrate between about 15° and about 30° C. per hour to a secondintermediate forming temperature sufficient to solidify said processmixture; (a4) annealing said process mixture, following said step ofcooling from said first intermediate forming temperature, at anannealing temperature between about 600° and 670° C. in an atmospherecontaining oxygen and for a time period greater than about 3.5 hours;(a5) cooling said process mixture from said annealing temperature to athird intermediate forming temperature less than about 400° C. at acooling rate between about 15° and about 30° C. per hour; and (a6)adding Na₄ P₂ O₇ to said process mixture at a fourth intermediateforming temperature greater than about 1300° C. but less than said firstintermediate forming temperature; and (b) subjecting said intermediateceramic mixture to a heat treatment comprising the steps of: (b1)heating said intermediate ceramic mixture to a first heat treatmenttemperature of between about 850° and 1000° C. at a heating rate ofbetween about 1° and 2° C. per minute; and (b2) sintering saidintermediate ceramic mixture at a sintering temperature between about850° and 1000° C. for a time period sufficient to increase the densityof said ceramic mixture to at least about 2.1 g/cm³.
 18. The process ofclaim 17 wherein said first intermediate forming temperature is betweenabout 1400° and 1500° C.,
 19. The process of claim 17 wherein saidsecond intermediate forming temperature is about room temperature. 20.The process of claim 17 wherein said time period for said annealing step(a4) is between about 3.5 and 5 hours,
 21. The process of claim 17wherein said third intermediate forming temperature is between about300° and 350° C.
 22. The process of claim 17 wherein said fourthintermediate forming temperature is greater than about 1350° C. but lessthan said first intermediate forming temperature.
 23. The process ofclaim 17 wherein said intermediate ceramic mixture is heated to saidfirst heat treatment temperature from about room temperature.
 24. Theprocess of claim 17 wherein said time period of said sintering step (b2)is between about 2.5 and 4 hours.
 25. The process of claim 17 whereinsaid heat treatment further comprises the step of cooling saidintermediate ceramic mixture to a temperature less than about 910° C.following said heat treatment.
 26. The process of claim 17 wherein saidamorphous ceramic glass has a density greater than about 2.5 g/cm³following said heat treatment.
 27. The process of claim 17 wherein saidprocess mixture comprises coal ash waste; a waste material comprisingborax or boric acid manufacturing plant waste; and titanium pigmentwaste.
 28. The process of claim 17 wherein said process mixture furthercomprises between about 1 and 4% by weight of K₂ O and Na₂ O in total,and between about 2 and 11% by weight Fe₂ O₃ and FeO in total.
 29. Theprocess of claim 17 further comprising the step of molding saidintermediate process mixture at a molding temperature sufficient toliquify said process mixture for pouring into a mold but less than saidfirst intermediate forming temperature, said step of molding followingsaid step (a5) of cooling from said annealing temperature.
 30. Theprocess of claim 29 wherein said molding temperature is between about1360° and 1400° C.
 31. The process of claim 29 further comprising a stepof cooling said process mixture to about room temperature following saidstep (a5) of cooling from said annealing temperature but prior to saidstep of molding.
 32. The process of claim 17 wherein said intermediateceramic mixture comprises:between about 35 and 55% by weight SiO₂ ;between about 18 and 28% by weight Al₂ O₃ ; between about 1 and 5% byweight CaO; between about 7 and 14% by weight MgO; between about 0.5 and5% by weight TiO₂ ; between about 0.4 and 3% by weight B₂ O₃ ; andgreater than 0 and up to about 1% by weight P₂ 5₅.
 33. The process ofclaim 17 wherein said process mixture comprises:between about 35 and 55%by weight SiO₂ ; between about 18 and 28% by weight Al₂ O₃ ; betweenabout 1 and 5% by weight CaO; between about 7 and 14% by weight MgO;between about 0.5 and 5% by weight TiO₂ ; between about 0.4 and 3% byweight B₂ O₃ ; and greater than 0 and up to about 2% by weight Na₄ P₂O₇.